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VEGETABLE CELLS.

nates, which attracts a small portion of the mucilaginouscontents, and becomes wholly clothed by it: on the surfaceof the mucilaginous layer the cell-membrane originates.

In the other cases of free cell-formation, nothing canbe seen of nuclei during the whole process. Either nonucleus really exists, or it withdraws itself from vision,through relatively minute size, or agreement of densitywith the density of the contents of the young cell. Inthe first case we must assume, that a definite portion ofthe contents of the parent-cell may independently becomeindividualized and converted into a cell. In the secondcase, the process would be the same as in the endosperm-cells. In my opinion a rigid distinction must be madebetween normal and abnormal cell-formation, in solvingthis question. By normal cell-formation I understandsuch as is necessarily connected with the vegetative andreproductive processes in a plant, and which always pro-ceeds according to laws definitely laid down for eachplant. By abnormal cell-formation, on the other hand,I understand such as is not directly and necessarily con-nected with the vegetative and reproductive processes,and must always be regarded more or less as producedby the action of external influences interrupting theregular course of the life of the cell.

As to the abnormal cell-formation in the cells of Alga:,I am convinced that no nuclei ever take part in it. Forthis kind of cell-formation is united by every possibleintermediate stage, with a process in which the formationof nuclei cannot enter into the question. In the firstpart of this Essay* I have mentioned a partial formationof membrane where, in consequence of disturbing externalinfluences, the mucilaginous layer is retracted in placesfrom the cell-wall, and becomes coated with new piecesof membrane. This process is of course independent ofthe influence of any nucleus. I, at the same time, statedthat the mucilaginous layer sometimes becomes detached

* Ray Translation, pp. 208 et seq.